Data encryption and decryption is in the spotlight, and data encryption and decryption is an important requirement in communication technology. Recently, with the popularity of personal digital devices such as smartphones, audio is gradually becoming the mainstream of communication media. In this situation, there is an increasing need for an audio signal encrypting and decrypting process. An encrypting and decrypting algorithm based on public keys and private keys may be mainly used for audio signal encryption and decryption. In the encrypting and decrypting algorithm based on public keys and private keys, a transmitter must use a public key of a receiver to encrypt an audio signal. After the audio signal is encrypted, only the receiver that has previously provided the public key may decrypt the audio signal by using its private key. However, a method of using the encrypting and decrypting algorithm based on public keys and private keys is costly. Moreover, in a case where several persons communicate with each other as in WeChat, the cost may increase significantly and the confidentiality of information transmission may not be guaranteed.